prezto/modules/pacman/functions/pacman-list-disowned

#
# Lists Pacman disowned files.
#
# Authors:
#   Benjamin Boudreau <dreurmail@gmail.com>
#   Sorin Ionescu <sorin.ionescu@gmail.com>
#

local tmp="${TMPDIR:-/tmp}/pacman-disowned-$UID-$$"
local db="$tmp/db"
local fs="$tmp/fs"

mkdir "$tmp"
trap  'rm -rf "$tmp"' EXIT

pacman --quiet --query --list | sort --unique > "$db"

find /bin /etc /lib /sbin /usr \
  ! -name lost+found \
    \( -type d -printf '%p/\n' -o -print \) | sort > "$fs"

comm -23 "$fs" "$db"